The invention is directed to improvements in fuel injection pumps.
One such pump is known from U.S. Pat. No. 4,127,366. In that fuel injection pump, fuel is pumped via a pressure valve into a conduit of a pressure valve holder by a pump piston driven to reciprocate in a cylinder bore; in the cylinder bore, this piston encloses a pump work chamber, and the piston is rotatable about its axis for fuel quantity distribution. The pressure valve holder connects the pump element, which receives the pump cylinder and the pump piston, to the injection line, which in turn connects the injection pump and injection nozzle with one another. A pressure valve spring disposed in an axial recess in the pressure valve holder and closing the pressure valve in the direction of the pump work chamber is supported on a support part that rests on the end face of the axial recess into which the conduit to the injection line discharges. In the known fuel injection pump, the support part is a circular-cylindrical disk, from which an axial protrusion serving to guide the valve spring projects. The face end of the recess is adapted to the cylindrical shape of the support part and thus has an abrupt transition from the large diameter of the recess to the smaller diameter of the conduit. As the demands for injection pressure increase, increasing loads on material arise because of the incident high injection pressures of up to 1300 bar. These pressures arise especially in the high-pressure regions, that is, in the pump work chamber and the parts through which fuel flows at high pressure. Hence the fuel flows at high pressure via the opened pressure valve through the recess of the pressure valve holder and in so doing exerts a high pressure upon the inner wall of the housing. With the increasing load via the injection pressure upon successive working strokes of the pump piston, peaks of tension occur at the sudden change in diameter because of a notching effect that causes fissuring, which in turn causes breaks and the resultant disruptions to fuel injection pump function.